1. Field of the Invention
The present invention relates to an image sensor, and a ranging apparatus and an imaging apparatus including the same.
2. Description of the Related Art
In a digital still camera or a video camera, technologies for detecting distances for automatic focusing (AF) are known. With regard to such technologies for detecting distances for AF, Japanese Patent Application Laid-Open No. 2009-158800 proposes a ranging apparatus in which a part of pixels of an image sensor have a ranging function and the detection is made by a phase difference system. The phase difference system is a method of comparing images of light fluxes that have passed through different regions on a pupil of an imaging optical system, and employing triangulation using stereo images to detect a distance. With this method, unlike the case of a related-art contrast system, it is not necessary to move a lens to measure the distance, and thus high-speed and high-accuracy AF is possible. Further, real-time AF is possible when moving images are taken.
As a configuration example of a ranging pixel, a configuration illustrated in FIGS. 9A and 9B is known. A ranging pixel 900 includes a microlens 901, a waveguide 902 (including a core 903 and a clad 904), and photoelectric conversion units 905 and 906 provided in a substrate 909. The microlens 901 has focusing positions at positions of the respective photoelectric conversion units 905 and 906. With such a configuration, a light flux 911L that has passed through a partial pupil region 910L on a pupil of an imaging optical system 910 is guided to be received by the photoelectric conversion unit 906, and a light flux 911R that has passed through another pupil region 910R is guided to be received by the photoelectric conversion unit 905. Such a characteristic of the ranging pixel to receive the light flux from a partial region on the pupil is called a pupil division characteristic. Based on signals acquired from those photoelectric conversion units 905 and 906 and known information on the pupil division characteristic, a distance to a ranging target is detected.
However, in FIGS. 9A and 9B, a part of the light flux that passes through the pupil region 910L to be collected by the microlens 901 may not be converted into light in a waveguide mode of the waveguide 902, but may become crosstalk light 912 to propagate through a nearby ranging pixel 900′. A large amount of crosstalk light 912 reaches a particularly closer photoelectric conversion unit 905′ of the nearby ranging pixel 900′. The photoelectric conversion unit 905′ is originally provided so as to acquire the light flux 911R from the pupil region 910R, and the pupil division characteristic changes when the photoelectric conversion unit 905′ also acquires the light flux 911L from the different pupil region 910L. Other photoelectric conversion units may similarly acquire a light flux from a pupil region different from a predetermined pupil region, which cause change in the pupil division performance. In this case, when the diaphragm of the imaging optical system or the ranging target changes, the angular range or wavelength of incident light may change, thereby causing change of the crosstalk light. With this, the pupil division characteristic may be changed from a predetermined characteristic, which may cause deterioration in ranging accuracy.